1. Field of the Invention
This invention relates to a levelling device of a roughness measuring machine, wherein a vertically movable stylus and an object to be measured are relatively moved to the left and right, with the both members being in contact with each other, and a vertical movement of the stylus is detected to measure a surface roughness of the object. The levelling device is of such an arrangement that changes in position between the object and displacement detecting means are performed such that a measured value does not scale out.
2. Description of Related Art
In general, the conventional roughness measuring machine has had the construction shown in FIG. 4.
As shown in a typified manner in FIG. 4, this roughness measuring machine has included: a base 1 having a flat and smooth top surface with an object W to be measured rested thereon; a column 2 erected on the base 1 in the direction of a Z-axis; a slider 3 being in engagement with a screw 4 provided at one end thereof with a handle 9 and vertically movable in the direction of Z-axis relative to the column 2; a movable member 6 movable by X-axis drive means, not shown, which is incorporated in the slider 3; a head 7 supported by the movable member 6; displacement detecting means 11 housed in the head 7; and a casing 8 including a measuring circuit, a control-operational circuit, display means and the like. The displacement detecting means 11 includes: a cross spring 14 secured to the head; an arm 13 rotatable about this cross spring; a stylus 12 provided on the forward end of the arm 13; and a displacement detector 15 formed of a differential transformer construction for example, which detects a vertical displacement of the stylus 12 by catching a tilt of the arm 13 when the stylus 12 vertically moves due to the surface roughness of the object W. Accordingly, when the object W is set onto the base 1, the handle 9 is operated to lower the slider 3 to thereby bring the stylus 12 into contact with the object W, and thereafter, the X-axis drive means is operated to move the stylus 12 and the object W relative to each other in the direction of X-axis (in this conventional example, the stylus 12 is moved), a displacement signal due to the vertical movement of the stylus 12 from the displacement detector 15 of the displacement detecting means 11 is inputted through a cable into the measuring circuit housed in the casing 8, where predetermined calculations and the like are performed, to thereby search the surface roughness of the object W as a measured value. The respective roughnesses corresponding to the positions of the object W in the direction of X-axis were able to be continuously enlargedly displayed on the display means formed of a CRT, and further, be stored in a blank.
However, the conventional roughness measuring machine has presented the following disadvantages.
More specifically, when the displacement detecting means 11 (head 7) and the surface of the object W are in parallel to each other in the lateral direction as shown in FIG. 5(A), on the display means (or on the storage blank), the measured values were able to be displayed with a scope between the upper limit value and the lower limit value, which has predetermined widths from a preset base line. However, for example, when the displacement detecting means 11 (head 7) is tilted due to the place of installation of the base 1 or the object W itself has a tilted surface (FIG. 5 shows a case where the object W has the tilted surfaces), such a disadvantageous situation was brought about that, even if the surface roughnesses of the object W appear as shown in FIG. 5(A), the measured value scales over the upper limit value or the lower limit value due to the fact that the center locus tilts to the base line as shown in FIGS. 5(B) or 5(C). This fact is caused by the construction wherein the displacement detecting means 11 detects a vertical displacement of the stylus 12 by the utilization of a tilt angle of the rotatable arm 13.
For this reason, in the past, while such preparations were made that the base 1 was set with the top surface thereof being positioned horizontally, whereby the displacement measuring means 11 (head 7) was able to move horizontally, measuring was tried to be conducted on the object W, which is rested on the base 1 over a predetermined length to be measured. When the measured value scaled over the upper limit value or the lower limit value, or there were such possibilities, the position of the object W was corrected, i.e. levelling work was performed. A roughness to be measured is in the order of micron meter, while, a measuring length is as long as several mm. Moreover, these data are to be enlarged to 50-1000 times for displaying in the display means. Accordingly, the levelling work is a so-called groping work, so that a fairly high skill level is required. Furthermore, even for a skilled worker, it is necessary to perform several times of levelling work, so that much labor and time are necessitated to spend, thus resulting in the disadvantages of that the operating efficiency and the production efficiency of the products are deteriorated and the economic burden is very high.